Rails core - Oct 2014 - Using "rescue_from Exception" to render a 500 page with the application layout will not catch all Exceptions

I'm not really sure whether this is a doc bug or a regular bug, so I 
figured I would open a thread here to figure out which.

If you use `rescue_from Exception` to render a dynamic 500 page with your 
application layout, and the exception was triggered from the application 
layout to begin with, it will escape the dynamic error page and render the 
one in `public`. Granted, this sounds obvious, but the documentation for 
rescue_from states that "Exceptions raised inside exception handlers are 
not propagated up," when in this situation that's clearly not the case.

I have a reproduction of this issue here: 
https://github.com/timraymond/rails-issue-rescue-from and a Docker image of 
it, if that's your cup of tea: 
https://registry.hub.docker.com/u/timraymond/rails-issue/ (docker pull 
timraymond/rails-issue). If you visit the "/explode" path, the
exception
raised there will be successfully caught by the dynamic 500 page. If you 
visit the "/greet/:name" path, it will escape the dynamic 500 page
because
of the exception raised in the application layout. The conditional in the 
layout is contrived, but is intended to represent complex logic that can 
trigger an exception in the layout when rendering some actions but not 
others.

I see in the edge guides that there's also a way to get this functionality 
by creating a route for "/500". I'm not sure if this would be
similarly
affected if an exception was raised by a layout, but it's something to 
consider as well, and perhaps someone who is more familiar with that 
feature can chime in :)

Let me know if I should open this up on GitHub as an issue, or if docrails 
needs to be updated to reflect that some exceptions can escape.

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